A display device that is mounted on the head and used for viewing an image, i.e. a head-mounted display (HMD), is widely known. The head-mounted display includes display units for left and right eyes, and is configured to be able to control vision and hearing when a headphone is used in combination. If it is configured such that when mounted on the head, the outside world is completely shut out, the effect of virtual reality at the time of viewing is enhanced. Also, the head-mounted display is capable of showing different images to the left and right eyes, and if images with a disparity are displayed to the left and right eyes, a 3D image may be presented.
The head-mounted display is a display system for presenting a virtual image to a user (that is, for forming a virtual image on the retina of an eye). Here, the virtual image is formed on the side of an object in a case the object is at a position closer to a lens relative to the focal length.
In the case of making a user view a virtual image, the distance, for example, to the user for whom the virtual image is formed is preferably changed depending on the image. For example, there is proposed a display device that presents a virtual image in a manner suitable for an image (for example, see Patent Document 1). This display device includes a magnifying optical system that arranges the same virtual image to be observed by the left eye and the right eye of the user on the same plane, and controls the distance between the virtual image and the user and the size of the virtual image according to the aspect ratio of the image. For example, with an image of a movie or a drama with an aspect ratio of 16:9 according to high vision broadcasting, a large virtual image is formed on the retina at a position about 15 meters away from the user, and with an image of a television signal with an aspect ratio of 4:3 according to an NTSC (National Television System Committee) method, a medium-sized virtual image is formed on the retina at a relatively close position of about 3 meters away from the user, and the user is allowed to feel a sense of presence, and also, a sense of fatigue felt at the time of viewing a virtual image is reduced.
If an appropriate angle of view is set by an optical system while using high-resolution elements such as EL (Electro-Luminescence) elements for display units of a head-mounted display for the left and right eyes, and multiple channels are reproduced by a headphone, a sense of presence of as if viewing in a movie theater may be realized.